1. Field of the Invention
The present invention relates to an information detecting apparatus and method and, particularly, to an information detecting apparatus and method for calculating, in accordance with past prediction values of codes, a prediction value of a code by using a given clock signal from a value of an analog signal corresponding to codes of a partial response format that constitute a predetermined, given pattern.
2. Description of the Related Art
In digital communication apparatuses, recording apparatuses, etc., codes of a partial response format, for instance, corresponding to given digital data are supplied via a predetermined medium. The received codes are detected as an analog signal, which is sampled while its amplitude, phase, etc. are adjusted in accordance with its phase and level. The signal is thereafter decoded, for instance.
An apparatus for receiving or reading out data of a partial response format is configured so as to be able to detect data even if a data point is not located at a peak point of a waveform by detecting and utilizing phase information and level information (amplitude information) of a supplied signal.
To detect a phase error and a level error of a signal as phase information and level information, respectively, a phase error .DELTA..tau..sub.n and a level error .DELTA..gamma..sub.n may be calculated according to the following equations: EQU .DELTA..tau..sub.n =-y.sub.n .multidot.x'.sub.n-1 +y.sub.n-1 .multidot.x'.sub.n EQU .DELTA..gamma..sub.n =(y.sub.n -x".sub.n).multidot.x'.sub.n +(y.sub.n-1 -x".sub.n-1).multidot.x'.sub.n-1
which were proposed by Mr. Roy D. Cideciyan et al. in "A PRML System for Digital Magnetic Recording," IEEE Journal on Selected Areas in Communications, Vol. 10, No. 1, January 1992. In the above equations, .DELTA..tau..sub.n represents a phase error (a phase difference between the clock signal and the reproduction signal) at time n, y.sub.n represents a signal value that is sampled at time n, and x'.sub.n represents a prediction value (judgment value) of an original code at time n, .DELTA..gamma..sub.n represents a level error at time n, and x".sub.n represents a signal peak value corresponding to the judgment value x'.sub.n.
Where the phase error and the level error are calculated in the above manner, a prediction value x'.sub.n of a code is calculated by using a value y.sub.n of the supplied signal.
It has also been proposed to detect phase information and level information at high speed by adding codes of a given pattern.
However, when an error occurs in prediction values of codes, phase information and level information that are calculated in the above-described manner are not correct and hence it becomes difficult to decode a supplied signal correctly. Further, when a phase error of a 0.5 period occurs due to a judgment error of a prediction value of a code of a partial response (1, 1) format, a long time will elapse until synchronization of the sampling is recovered in a PLL (phase locked loop) and the phase error is converged to a 0 or 1 period (integer period).